1587

ISSN 1229-9197 (print version)

ISSN 1875-0052 (electronic version)

Fibers and Polymers 2015, Vol.16, No.7, 1587-1594

Processing Technique and Uniformity Affecting Tensile Strength and

Hydrophobicity Properties of Glass Wool Felt

Yong Yang, Zhaofeng Chen*, Zhou Chen, Renli Fu, Yufang Li, and Cui Sheng1

College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China1College of Materials Science and Engineer, Nanjing Tech University, Nanjing 211800, P.R. China

(Received April 20, 2015; Accepted June 12, 2015)

Abstract: Glass wool felt (GWF) made from glass wool and phenolic resin adhesive is prospected to have a promising futurein sound insulation of aircraft. In this paper, the GWF was fabricated by centrifugal-spinneret-blow (CSB), and there weretwo different methods to guide the glass wool, which were free float type (FFT) and guided swing cylinder (GSC), with GSCbeing designed as uniform processes. The tensile strength and hydrophobicity properties of GWF from these two methodswere compared. The experimental results suggested that tensile strength and hydrophobicity properties of GWF by GSC weregreater, with non-uniformity being 5 %. The tensile strength, breaking length and elastic deformation of GWF were obtainedduring the GWF manufactured by GSC with fibers being in 2-D distribution, and the phase difference of the swing cylindersbeing π/2+2kπ. The maximum static contact angle and minimum water repellency of GWF produced by GSC were 141 o and15 g, while for FFT they were 100 o and 26.92 g, respectively. The uniformity of GWF’s smooth surface was accompanied byexcellent hydrophobicity.

Keywords: Glass fiber felt, Tensile strength, Hydrophobicity, Swing cylinder

Introduction

Glass wool felt (GWF) was manufactured from a set of

disordered fibers which is consolidated by local thermal

fusion or chemical binders, depending on the processing

technique. Goryainov et al. [1] stated that GWF could be

produced by centrifugal-spinneret-blow (CSB) and flame

attenuation processes, and the efficiency of the finished

products mainly depended on the manufacturing process, the

weight density of raw glass wool and the content of resin.

Compared to flame attenuation process, the CSB process

had more advantages, including low cost, high productivity,

uniformity and flexibility. Ku et al. [2] stated that the

selection of suitable processing techniques and parameters

could get optimum composite products. Champagne et al.

[3] and Liu et al. [4] presented that the characters of raw

glass wool, such as fiber diameter, fiber length and distribution,

closely depended on the parameters of CSB process. The

mechanical behavior of GWF was very different from that of

woven materials, their stiffness and strength were lower than

their woven counterparts, but they were far superior in terms

of their deformation capability and energy absorption during

deformation. Physical and mechanical properties of GWF

were complex, and more experiments and numerical simula-

tions were developed to gain a better understanding of the

mechanical performance. Cox et al. [5] presented a two-

dimensional random networks to analysis the effect of

orientation of the fibers on the stiffness and strength of paper

and other fibrous materials, and it was shown that these

effects were presented completely by the first few coefficient of

the distribution function for the fibers in respect of orientation.

Yang [6] and Rigdahl et al. [7] developed a model for a two-

dimensional network of randomly distributed fibers to predict

the elastic modulus, the stiffness of the bonds between fibers

was taken into account and found that the bond stiffness had

little influence on the elastic modulus. Heyden [8] presented

two-dimensional and three-dimensional periodic-cell models

for cellulose fiber, and it was found that the axial stiffness

of straight fibers was of greater importance than their

bending stiffness, and that transversal spring stiffness had a

stronger influence than rotational or normal spring stiffness.

Venkateshwaran et al. [9] used Rule of Hybrid Mixture to

predict the tensile strength and modulus of short, randomly

oriented hybrid-natural fiber composite. It was observed

that the values of predicted tensile properties of hybrid

composites were little higher than experimental values.

Ridruejo et al. [10] analyzed the deformation and damage

micromechanisms of a glass-fiber non-woven felt, and found

that fracture began by interbundle bond fracture, followed

by frictional sliding between bundles, leading to the localization

of damage in a wide band. Rizvi et al. [11] explored the

influence of microstructure on the mechanical behavior of

fibrous material, and the randomness of fiber orientation

made the fibrous structure more flexible at the cost of lower

strength, the measured mechanical properties of a fibrous

matrix were also observed to be dependent on sample size.

Kulachenko et al. [12] explored the elastic properties of

cellulose nanopaper, and found that the effect of the drying

could not solely explain the relatively low elastic modulus of

nanopaper, the most influence were the presence of non-

crystalline regions along the length of the nanofibers, initial

strains and the three-dimensional structure of individual

bonds. Borodulina et al. [13] investigated a relation between

micromechanical processes and the stress-strain curve of a*Corresponding author: zhaofeng_chen@163.com

DOI 10.1007/s12221-015-5310-1

1588 Fibers and Polymers 2015, Vol.16, No.7 Yong Yang et al.

dry fiber network during tensile loading, the results showed

that failed bonds were located in the places with high local

strain, the width of strain concentrations regions had a size

on a millimeter scale and depended on the initial details of

the network structure, such as local fiber orientations and

bond density.

In the traditional CSB, the glass wool floated freely and

the distribution of fibers was random, which led to very

uneven GWF formation. At the same time, since the uniformity

affected the physical and mechanical properties of GWF,

optimizing the technique of glass wool floating was one of

the most important priorities. Till date, there are few reports

published on uniformity of the CSB process. In this article,

swing cylinders were used to improve the uniformity of

GWF. The method of superposition was discussed, and the

physical and mechanical properties of GWF with different

processes were contrasted.

Experimental

Raw Materials

GWF was made from pure glass wool and phenolic resin

adhesive. The density, thickness and quantity of the resin

used were 10 kg/m3, 25 mm and 18 %, respectively. The

diameters of glass wool were mainly concentrated in 2-

4 μm, and the mean diameter of glass wool was 3 μm.

Preparation Technology

Figure 1 is the schematic diagram of CSB process. Vitreous

fluid flowed out from the leak board and formed a vitreous

fluid stream. Then the primary glass fibers were formed

through pores on centrifugal pan’s surrounding wall by

making use of centrifugal force. These primary glass fibers

were immediately affected by air current jetted from ring-

form combustion nozzles arranged concentrically with the

centrifugal pan, which were then further split and stretched

into secondary fibers, namely, glass wool [14]. The glass

wool with phenolic resin adhesive was sent into curing

furnace where GWF was formed.

The fibers with free float type (FFT) and guided swing

cylinder (GSC) were utilized to manufacture GWF in this

paper. Figure 1(a) is FFT that glass wool float freely. Figure

1(b) is GSC that glass wool pass though the swing cylinder

and the trajectory of swing cylinder is similar to simple

pendulum movement. Glass wool fell onto the conveyor belt

by the guide of swing cylinder, and the plane of swing

cylinder movement was perpendicular to the direction in

which the conveyor belt moved.

Measurements

Uniformity

In order to quantify the uniformity of material, coefficient

of variation (CV) was calculated by the weight of samples.

CV reflects the non-uniformity rate of fiber materials which

is defined by:

(1)

where σ is expressed as:

(2)

where CV is the coefficient of variation, σ is mean square

error of sample, is arithmetic mean of the sample, n is the

number of samples, Xi is density of each sample.

In this test, each group of the samples were delivered from

the production line and divided into 25 pieces with equal

size in the same group, and the size of samples were

200 mm×200 mm×25 mm.

Tensile Strength

Tensile strength was measured on a universal material

testing machine (HOUNSFIELD H10KS) by standard FED-

STD-191, Method 5100. During tensile test, the stretching

speeds of the cross head were all set to be 305 mm±13 mm/

CVσ

X

---- 100%×=

σΣi 1=

n

Xi X–( )2

n 1–--------------------------------=

X

Figure 1. Schematic diagram of CSB process; (a) free float type

(FFT) and (b) guidance with swing cylinder (GSC).

Figure 2. Illustration of the mechanical test on a universal testing

machine; (a) schematic diagram and (b) tensile test.

Processing Technique and Physical Property of Glass Wool Felt Fibers and Polymers 2015, Vol.16, No.7 1589

min, the samples with different processes were tested five

times. In the testing, it should make sure that samples did not

slip and fractured far from the clamps. Illustration of the

mechanical property test on the testing machine is shown in

Figure 2.

Hydrophobic Properties

Static contact angle was measured on the static contact

angle testing machine (VCA Optima/VCA 3000S) [15].

To estimate water repellency, three specimens of nominal

size 254 mm×254 mm were cut and equally spaced across

the width of GWF. Afterwards the specimens were floated

on the surface of water. A rigid screen with 6.35 mm mesh

was placed on top of specimens and slowly submerged to a

level 127 mm below the surface. After 15 min, the screen

was released and the specimens were raised slowly until the

specimens floated. By means of a spring clamp, each specimen

was gripped at the corner and hung in vertical position for

60±5 s. Afterwards, the weight and water content of each

specimen were determined.

Morphological Investigations

The distribution and orientation of glass wool in GWF,

and interfacial adhesion between resin and glass wool were

morphologically investigated using SEM at 20 kV accelerating

voltage [16,17].

Results and Discussion

Theoretical Analysis of Uniformity

In the FFT, the glass wool floated freely, and the distribution

of fibers were random. Compared to FFT, glass wool passed

through swinging cylinder and the falling trajectory was

similar to a simple pendulum movement in the GSC. The

trajectory of glass wool on the conveyor belt was sine or

cosine curve. Viggo Tarnow [18] constructed a three-dimensional

coordinate system to accurately analyze GWF, and directions in

the GWF were described by a three-dimensional coordinate

system. The X axis was perpendicular to the conveyor belt,

the Z axis was in the direction of the moving conveyor belt,

and the Y axis was perpendicular to the two other axes. The

plane of swing cylinder movement was X-Y. The schematic

diagram of the trajectory between the swing cylinder and

glass wool is described in Figure 3.

According to the number of swing cylinders and the

differences in the oscillation frequency, the different super-

imposed effects could be obtained. In this article, swing

cylinders with the same oscillation frequency were discussed.

According to the principle of superposition, the more number

of swing cylinders there were, the better the superimposed

effect was. For one centrifuge pan and one swing cylinder,

the trajectory of glass wool is depicted in Figure 4.

According to Figure 4, the trajectory equation of glass

wool is as follows:

Y=Asin(ωt + ϕ) (3)

where Y is displacement, A is amplitude which equals to the

biggest displacement of the trajectory of glass wool, ω is

angular frequency of swinging cylinder, t is time and ϕ is

phase.

Figure 3. Schematic diagram of the trajectory between swing

cylinder and glass wool.

Figure 4. The trajectory of glass wool with one swing cylinder.

Figure 5. Different superimposed effect with two swing cylinders;

(a) 1# GSC and (b) 2# GSC.

1590 Fibers and Polymers 2015, Vol.16, No.7 Yong Yang et al.

When the number of swing cylinders was more than one,

the trajectory of glass wool could be superimposed. According

to the phase difference and the number of swing cylinders,

different superimposed effects could be obtained. According

to the production of experimental conditions, two swing

cylinders were used to produce GWF in actual production

line. In this case, the most important and best ways of

superimposition are in Figure 5. This process is defined as

1# GSC and 2# GSC in Figure 5(a) and Figure 5(b),

respectively.

Uniform Performance

The GWF were manufactured by FFT and GSC, and the

uniform performance of the GWF from these two methods

were examined and compared. The data of non-uniformity is

described in Figure 6, and the appearance of GWF is shown

in Figure 7. Obviously, there were some blind pores in the

surface of the sample produced by FFT, and the uniformity

of the sample from GSC was superior to FFT. The mean data

of non-uniformity for FFT sample was 10 % and while non-

uniformity of method 1# of GSC was closed to 8 % and for

method 2# of GSC was half of FFT’s. Phase difference of

1# GSC with two swing cylinders was π +2kπ, and the

superimposed section of GWF was mainly limited to the

middle part of conveyor belt, however the glass wool was

relatively small at intervals. Compared to the middle part,

the edging portion of GWF was distributed unevenly in the

production. Phase difference of 2# GSC was π/2+2kπ. The

superimposed section of glass wool almost covered the

whole conveyor belt. The fibers of GWF with smooth

surface were distributed more uniformly. Sirok et al. [19]

and Blagojevic et al. [20] researched the relations between

the parameters of mineral wool production and mineral wool

distribution, and they found the uniform mineral wool

distribution in the primary layer significantly affected the

final product quality. The uniformity affected the physical

and mechanical properties of GWF and hence through GSC,

excellent uniformity with phase difference of π/2 +2kπ

could be obtained.

Tensile Strength

The relationship between tensile strength and breaking

length of GWF is plotted in Figure 8. It was obvious that

tensile strength increased simultaneously with breaking

length. The tensile strength for the GWF with GSC was

much higher than those with FFT. Glass wool passed through

swinging cylinder, and part was guided into a small amount

fiber bundle on the surface of GWF. The bundle fiber played

Figure 6. The data of uniformity of GWF by both FFT and GSC.

Figure 7. GWF with FFT versus GSC’s; (a) FFT, (b) 1#GSC, and (c) 2# GSC.

Figure 8. Tensile strength versus fragment length of GWF.

Processing Technique and Physical Property of Glass Wool Felt Fibers and Polymers 2015, Vol.16, No.7 1591

an important role in this improvement and it was equivalent

to a small amount of strengthened fibers to enhance the

strength of GWF, which allowed the GWF to have high

force transfer length along the fiber bundle. Fridrikh et al.

[21] and Tan et al. [22] stated that the measurements and

subsequent calculations had most often followed methodologies

used to describe the mechanical strength of bulk solids,

which might not be appropriate for fibrous materials because,

unlike bulk solids, the properties of fibrous materials depended

not only on the material of the bulk solid, but also on the

structure of the matrix, e.g. fiber diameter, fiber curvature,

fiber alignment, fiber density. Tensile strength and Young’s

modulus of the material were directly affected by the fiber

length distribution function and fiber orientation. Thomasson et

al. [23] suggested that composites with longer glass fibers

usually had greater stiffness and strength than those with

shorter glass fibers. However, in this paper, the fiber length

distribution function was constant, and the fiber orientation

was changed along with the different processes. The GSC

was observed to have higher arrangement level of fibers as a

result of having two-dimensional distribution, conversely to

the random distribution such as three-dimensional distribution

in FFT. This phenomenon is shown in Figure 9, where that

the fibers with two-dimensional distribution exhibited high

tensile strength, compared to the three-dimensional distribution.

Most fibers with two-dimensional distribution lay in the

same plane, and while the fibers were fused to each other,

the friction between the fibers was not ignored. Therefore,

the fibers that spanned the entire GWF longitudinally could

bear the tensile load.

The tensile force versus elastic deformation of different

samples by FFT and GSC are shown in Figure 10. The results

shown that there were a large difference in appearance of

these curves, the reasons were that fibrous materials existed

non-uniform feature in the process of preparation, and in the

Figure 9. SEM micrographs of GWF; (a) FFT and (b) GSC. Figure 10. The tensile force versus deform length of GWF.

1592 Fibers and Polymers 2015, Vol.16, No.7 Yong Yang et al.

test the samples did not slip and fractured far from the

clamps, however the different distances between breaking

point and clamps led to difference curves. The elastic

deformation reached a maximum value corresponding to the

biggest tensile force. The length of elastic deformation of

FFT and GSC were 3-6 mm and 6-8.7 mm, respectively. The

elastic deformation of GSC was larger than FFT. The elastic

deformation of GWF was dependent on the curvature of the

length of the longest fiber. The fibers in three-dimensional

were curved, and provided very little tensile force. The

uniformity, the fiber bundle and the arrangement level of

fibers led to the GWF with large elastic deformation.

These results were consistent with the uniform values of

the samples and the process of GSC. Usually, GWF with

higher uniformity translated into higher tensile strength,

breaking length and elastic deformation. There was a significant

improvement in physical properties and tensile strength by

addition of swing cylinder.

Hydrophobic Properties

Static Contact Angle

The static contact angle referred to the phenomenon where

water droplets fell onto a level solid surface. Latva-Kokko et

al. [24] stated that the wetting ability was controlled by the

pairwise interfacial energies of the two fluids and the solid,

and it could be characterized by a contact angle. The contact

angle was the angle formed by the intersection of the interfaces

bounding the three phases. The tangent of solid-liquid interface

and gas-liquid interface clamp the liquid phase in the

formation of the angle as shown in Figure 11.

Dimitri et al. [25] stated that the relation between contact

angle and surface tension is as follows:

(4)

where θe is the measured contact angle and γ is the surface

energy of the solid-vapor (SV), solid-liquid (SL) and liquid-

vapor (LV) interface.

The shape of the droplets on the GWF by FFT and GSC

are shown in Figure 12. It could be seen that water droplets

on GSC was spherical, and FFT was semi-spherical. Table 1

shows the contact angle and adhesion work of GWF with

different processes. The ways of superposition did not change

the contact angle and adhesion work. Besides, contact angle

and adhesion work changed with different processes. It

could be inferred from Table 1 that the processing of GSC

was considerably greater than the processing of FFT. The

use of swinging cylinder improved the hydrophobic properties

of GWF, such as the contact angle and adhesion work.

Water Repellency

Water repellency of GWF is shown in Figure 13. It could

be seen from the figure that water content of GSC was lower

than FFT’s. However the variance of water content of

different samples with FFT and 1#GSC was larger whiles

2#GSC’s was more stable. This phenomenon was mainly

γLVcosθe γSV γSL–=

Figure 11. Static contact angle.

Figure 12. The contact angles of GWF with different processes;

(a) FFT, (b) 1#GSC, and (c) 2# GSC.

Table 1. The contact angle and adhesion work of different GWF

Samples The contact angle (º) Adhesion work (J)

FFT 100 26.92

1#GSC 140 17.04

2#GSC 141 16.49

Processing Technique and Physical Property of Glass Wool Felt Fibers and Polymers 2015, Vol.16, No.7 1593

due to the uniformity of GWF. During the test procedure,

water was mainly absorbed into the interior of GWF leading

to high water content. In the FFT, there were some blind

pores in the surface. The profile of blind pores increased the

area of suction and had certain function for storing water.

Water content of 1#GSC and 2#GSC were close to each

other though 2#GSC was slightly better than 1#GSC. Firstly,

fiber bundle and two-dimensional distribution made GWF

with smooth surface, whereas high uniformity led a small

amount closed pores. Secondly, large contact angle and small

adhesion work made GWF with strong water repellency. This

was why the water repellency of 2#GSC was superior to that

of 1#GSC and FFT. In other words, water content decreased

with addition of uniform GWF.

Conclusion

In this paper, GWF was fabricated by means of centrifugal

process, and there were two different methods to guide the

glass wool, which were free float type (FFT) and guided

swing cylinder (GSC). The uniformity affected tensile

strength and hydrophobicity properties of GWF, and the best

uniform process was the swing cylinders with phase difference

of π/2+2kπ. The tensile strength for the GWF with GSC was

much higher than those with FFT. Glass wool passed

through swinging cylinder, and part was guided into a small

amount fiber bundle on the surface of GWF leading to

enhance the strength of GWF. In these processes, the GSC

had higher arrangement level of fibers as a result of having

two-dimensional distribution, conversely to the random

distribution such as three-dimensional distribution in FFT.

Fibers with two-dimensional distribution lay in the same

plane and fused to each other, the friction between the fibers

improved the tensile strength of samples.

The maximum static contact angle and minimum water

repellency of GWF by GSC were 141 o and 15 g, in contrast

to FFT which were 100 o and 26.92 g, respectively. The

results showed that water droplets on GSC was spherical,

FFT was semi-spherical, and water content of GSC was

lower than FFT’s. In the FFT, there were some blind pores in

the surface, and the profile of blind pores increased the area

of suction and had certain function for storing water. Fiber

bundle and two-dimensional distribution made GWF with

smooth surface, whereas high uniformity led a small amount

closed pores, and large contact angle and small adhesion

work made GWF with strong water repellency. A better

uniformity improved tensile strength and hydrophobicity,

and it was demonstrated that optimizing the processes

improved uniformity greatly, obtaining GWF with stable

physical and mechanical properties.

Acknowledgements

Thanks the finial support of Jiangsu Collaborative Innovation

Center for Advanced Inorganic Function Composites. This

work was also supported by Major Achievements of Jiangsu

Province (BA20130987) and Development of Vacuum

Insulation Panel of China Building Cooperative Research

(2015DFI53000), respectively.

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